On Wed, Aug 16, 2023 at 08:51:49PM +0200, David Hildenbrand wrote:
> On 16.08.23 20:41, Matthew Wilcox wrote:
> > On Wed, Aug 16, 2023 at 03:33:30PM +0200, David Hildenbrand wrote:
> > > My simple tests passed so far. If there isn't something obvious missing,
> > > I can do more testing and send this as an official patch.
> >
> > I think you missed one:
> >
> > +++ b/mm/swapfile.c
> > @@ -1490,7 +1490,7 @@ int swp_swapcount(swp_entry_t entry)
> >
> > page = vmalloc_to_page(p->swap_map + offset);
> > offset &= ~PAGE_MASK;
> > - VM_BUG_ON(page_private(page) != SWP_CONTINUED);
> > + VM_BUG_ON(page_swap_entry(page).val != SWP_CONTINUED);
>
> That falls under the "weird handling of SWP_CONTINUED using vmalloced
> pages". So different user of page_private().
>
> Note that we don't even store swap entries in there but extended swap
> counts.
Ah, right. I see now.
Not necessarily as part of this patch, but it got me wondering ...
should we do this? And then maybe we could remove folio_swap_entry()
and folio_set_swap_entry() and just use folio->swap directly.
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3880b3f2e321..e23d1356e504 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -266,6 +266,14 @@ static inline struct page *encoded_page_ptr(struct encoded_page *page)
return (struct page *)(~ENCODE_PAGE_BITS & (unsigned long)page);
}
+/*
+ * A swap entry has to fit into a "unsigned long", as the entry is hidden
+ * in the "index" field of the swapper address space.
+ */
+typedef struct {
+ unsigned long val;
+} swp_entry_t;
+
/**
* struct folio - Represents a contiguous set of bytes.
* @flags: Identical to the page flags.
@@ -276,7 +284,7 @@ static inline struct page *encoded_page_ptr(struct encoded_page *page)
* @index: Offset within the file, in units of pages. For anonymous memory,
* this is the index from the beginning of the mmap.
* @private: Filesystem per-folio data (see folio_attach_private()).
- * Used for swp_entry_t if folio_test_swapcache().
+ * @swap: Used for swp_entry_t if folio_test_swapcache().
* @_mapcount: Do not access this member directly. Use folio_mapcount() to
* find out how many times this folio is mapped by userspace.
* @_refcount: Do not access this member directly. Use folio_ref_count()
@@ -319,7 +327,10 @@ struct folio {
};
struct address_space *mapping;
pgoff_t index;
- void *private;
+ union {
+ void *private;
+ swp_entry_t swap;
+ };
atomic_t _mapcount;
atomic_t _refcount;
#ifdef CONFIG_MEMCG
@@ -1158,14 +1169,6 @@ enum tlb_flush_reason {
NR_TLB_FLUSH_REASONS,
};
- /*
- * A swap entry has to fit into a "unsigned long", as the entry is hidden
- * in the "index" field of the swapper address space.
- */
-typedef struct {
- unsigned long val;
-} swp_entry_t;
-
/**
* enum fault_flag - Fault flag definitions.
* @FAULT_FLAG_WRITE: Fault was a write fault.
diff --git a/include/linux/swap.h b/include/linux/swap.h
index bb5adc604144..59b0f37eae5b 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -335,13 +335,12 @@ struct swap_info_struct {
static inline swp_entry_t folio_swap_entry(struct folio *folio)
{
- swp_entry_t entry = { .val = page_private(&folio->page) };
- return entry;
+ return folio->swap;
}
static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry)
{
- folio->private = (void *)entry.val;
+ folio->swap = entry;
}
/* linux/mm/workingset.c */
